ARM: dts: dra7x-evm: Don't use dcan1_rx.gpio1_15 in DCAN pinctrl

Rev.F onwards ball G19 (dcan1_rx) is used as a GPIO for some other
function so don't include it in DCAN pinctrl node.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>